Most of the thermoplastic films used in the packaging of food products which must be kept in refrigerated environments, and particularly the stretchable films, undergo abrupt changes of their chemical and physical characteristics, particularly their elastic and plastic characteristics, at the low temperatures which must be maintained even during the packaging of such products, and become extremely fragile, with a risk of tearing during the stages of pre-stretching and/or stretching to which such films are normally subjected when in use. The threshold of practical risk varies with the chemical composition of the film, for example according to whether it is made of polyethylene (PE) or polyvinyl chloride (PVC), and rises exponentially with a decrease in temperature.